When a plurality of sub-devices are connected to ports connected to a host, the host uses a selective suspend mode to reduce power consumption. For example, when a USB network device connected to the host maintains an idle state during a certain time, the host operates only a port to which the USB network device is connected in a suspend state without influencing an operation of different ports connected to a USB root hub.
However, when the USB network device operates in a selective suspend mode, a USB network driver is in an intermediate sleep state D2, and does not receive a packet from a Transmission Control Protocol/Internet Protocol (TCP/IP) stack.